The present invention relates to an apparatus and method for discriminating among different types of optical discs. In particular, the present invention is directed toward a Fuzzy Inference System (FIS) for discriminating among single and double-layer DVDs and CD-ROMS.
Optical storage devices, such as digital versatile discs (DVD) are commonly used for storing large amounts of digital data on a single disc for use in audio/video or computer applications, and the like. To read this recorded data, a servo system focuses a laser beam onto the reflective surface of the disc such that the characteristics of the reflected beam allow the device to determine the recording format of the disc.
Different types of discs may have different refelectivities. CDs and DVDs have different track pitches and require different tracking servo system parameters. A CD, for example, having lower data density, may have a lower track pitch (tracks per inch or tpi) than the higher density DVD. An optical disc drive must be able to identify what type of disc has been loaded in order to properly read the disc. In addition, the optical disc drive should indicate when no media is present (or an unreadable disc has been inserted).
Newer and future optical disc drives may need to accept various types of disc formats such as CD-ROM (including computer CD-ROMs and musical CDs), CD-R (single write CDs), CD-RW (rewritable CDs) and DVDs (Digital Versatile Disc). DVDs may be available in more than one format, including single layer DVDs and double layer DVDs.
Most existing methods can only discriminate among some of the optical disc types, but not all. For example, in conventional DVD/CD players and recorders, prior art discrimination techniques can only discriminate among CD and DVD media. Other techniques may be able to discriminate among only some types of CDs. Moreover, many of these Prior Art techniques rely on a priori knowledge of the electromechanical properties of the laser, photo detector and the media.
For example, Kawasaki, U.S. Pat. No. 5,745,461, issued Apr. 28, 1998, and incorporated herein by reference discloses one technique where, with the optical head at a focus distance, the level of the reproduced signal is measured. CD and CD-Rs have different signal levels, and thus can be discriminated among one another. Ashinuma et al., U.S. Pat. No. 5,289,451, issued Feb. 22, 1994, and incorporated herein by reference, discloses a similar technique.
FIG. 1 is a block diagram illustrating the Prior Art technique of Kawasaki. A reflection measurement device 3 is provided on the opposite side to optical head 2 of optical disc 1 driven by a spindle motor. Reflection measurement device 3 measures reflectivity of back surface of optical disc 1 and may comprise a photo-reflector element. Measured reflectivity is output as reflectivity 101 of the disc surface and is supplied to microcomputer 6.
On the other side of optical disc 1, optical head 2, irradiating a laser light and approaching optical disc 1 for a focus searching operation, outputs a focus sum signal 102, which is also supplied to microcomputer 6 after being converted to a voltage level through focus sum signal converter 4. When optical head 2 is detected by focus sum signal 102 to have reached a focal area, a focus servo mechanism is actuated and optical head 2 is controlled through servo controller 10. After the focus servo mechanism is actuated, tracking signal 103 output from optical head 2 is also supplied to microcomputer 6 after being converted into a voltage level through tracking signal converter 5.
Microcomputer 6 determines whether optical disc 1 is single-sided or double-sided according to reflectivity 101. Microcomputer 6 further estimates the information density of optical disc 1 as well as the number and material of its recording layer(s) by 10 comparing intensity level of the focus sum signal 102 and the peak to peak value of the tracking signal 103 with corresponding values in a reference table. Microcomputer 6 also determines parameter values for initializing and mode-setting of the device, actuating a tracking servo mechanism of optical head 2 through servo controller 10.
Where optical disc 1 is assumed to have ID data recorded thereon from the above estimation, an attempt is made to read the ID data as a final confirmation before initialization or mode-setting. If, instead of ID data, optical disc 2 is estimated to have a wobble signal recorded on its track or to have a characteristic pattern of its synchronous signal in its reproduced signal, they are confirmed for final discrimination.
While the Kawasaki device may be able to discriminate among CDs and CD-Rs based upon signal levels, the apparatus may not be useful for distinguishing among other optical disc types.
Nemoto, U.S. Pat. No. 6,137,758, issued Oct. 24, 2000 and incorporated herein by reference, discloses an Optical Disc Discriminating Apparatus whereby an optical pickup irradiates a main beam and a pair of sub-beams onto an optical disc. Sub-beam pickups receive the sub-beam signals to produce a tracking error signal. The type of optical disc is determined by comparing the tracking error signal to a reference signal. This system requires the use of secondary tracking error beams and appears to be able to discriminate only among CD and DVD types of discs.
Even among those methods that purport to discriminate among all optical disc types, they may not be efficient, accurate, or fast. For example, another Prior Art technique, disclosed in Tsuchiya, U.S. Pat. No. 6,111,832, issued Aug. 29, 2000, and incorporated herein by reference, relies upon difference in thickness between the transparent layer and the reflective layer to discriminate between CD and DVD discs. Unfortunately, a high vertical deviation CD may appear to be a DVD using a method which relies on the difference in the thickness between the transparent layer and the reflective layer.
Another Prior Art technique, disclosed in Ryoo, U.S. Pat. No. 5,996,367, issued Oct. 12, 1999 and incorporated herein by reference, uses amplitudes of quad sum and focus error to discriminate CD verses DVD. The algorithm employed by Ryoo in using the amplitudes of quad sum and focus error to discriminate CD verses DVD may encounter discrimination problems since it relies on absolute amplitudes and offsets of the signals. These signals may vary from disc to disc and from drive type to drive type, and as a result may not produce consistent results in identifying disc types.
Another Prior Art technique, disclosed in Kamiyama, U.S. Pat. No. 5,909,419, issued Jun. 1, 1999 and incorporated herein by reference, relies upon track density difference to distinguish between CD and DVD discs. However, a high radial runout CD may look like a DVD when using an algorithm which relies on the track density difference between CD and DVD. In addition, recently developed high-density CDs are now available with a track density higher than that of prior CDs, but with a lower track density than typical DVDS. The algorithm of Kamiyama may be even less robust in distinguishing such high density CDs from DVDS.
Thus, a need still exists in the art for a technique which can accurately, reliably, quickly, and inexpensively discriminate among all types of optical discs.
Fuzzy logic systems are known in the art. The Fuzzy Logic Toolbox User""s Guide, Chapter 2, Foundations of Fuzzy Logic, incorporated herein by reference, discloses the basic techniques for applying fuzzy logic. Fuzzy logic may have particular applications to situations where a result of a logical operation is not always a uniform 0 or 1 value. To date, the inventor is unaware of application of fuzzy logic to the problem of disc type determination.
There are two basic types of Fuzzy Inference Systems (FIS) known in the Prior Art; The Sugeno-type and the Mamdani-type. A Sugeno-type first-order system may approximate the Mamdani-type, but require fewer system resources to implement.
Unlike the aforementioned Prior Art techniques, the present invention applies a cost-effective Fuzzy Inference System (FIS) algorithm which is capable of discriminating among various disc types including double-layer DVD, single-layer DVD, CD-ROM/CD-Audio, CD-R, and CD-RW.
A Fuzzy Inference System (FIS) is provided for the determination of an optical disc type in a DVD or other optical disc drive. This FIS optical disc determination algorithm relies on the physical properties of the reflecting layer of an optical disc, using a DVD and CD photo diode outputs, to discriminate among several disc types.
The FIS optical disc determination algorithm relies on the physical properties of the reflecting layer of an optical disc, using a DVD and CD photo diode outputs, to discriminate among several disc types. Focus error and quad sum data from both DVD and CD lasers is provided as eight inputs to a nineteen rule Sugeno FIS which outputs a value corresponding to drive type.